1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to an LCD for reducing power consumption and improving display quality.
2. Discussion of the Related Art
To display an image, an LCD controls optical transmissivity of liquid crystal cells according to a video signal. An active matrix LCD switches a data voltage supplied to liquid crystal cells using thin film transistors respectively formed at the liquid crystal cells to actively control data, and thus the active matrix LCD can improve display quality of moving images.
The LCD inverts the polarity of a data voltage charged in every group of a predetermined number of liquid crystal cells in order to reduce a DC offset component and degradation of liquid crystal. However, this inversion driving method increases the swing width of the data voltage supplied to data lines whenever the polarity of the data voltage is changed and raises a temperature of a data driving circuit. As a result, power consumption is increased.
A related art charge sharing method as shown in FIGS. 1A and 1B has been proposed to reduce the swing width of the data voltage, the temperature of the data driving circuit, and its power consumption, The charge sharing method turns on a charge share switch SW1 connected between neighboring output channels of the data driving circuit during a logic high period of a source output enable signal SOE to share positive charges and negative charges in a panel so as to change the initial output level of the data driving circuit to a middle level.
However, the related art charge sharing method cannot reduce power consumption of the data driving circuit all the time. The charge sharing method has an advantage of low power consumption when a data pattern having a large difference between output levels continuously output through a same channel is displayed. However, when a data pattern having a small output level difference is displayed, it is more effective for low power consumption to output the output voltages while maintaining previous output levels, as shown in FIGS. 2A and 2B, without using the charge sharing method.
The related art charge sharing method determines whether the charge sharing function is used irrespective of characteristics of a data pattern input to the data driving circuit, and uniformly applies the determination result to all data integrated circuits (data ICs) constructing the data driving circuit. In this case, data patterns in which difference of power consumption is large depending on whether the charge sharing function is used may be respectively input to different data ICs. Consequently, power consumption of a specific data IC increases compared to other data ICs. Thus, the conventional charge sharing method cannot achieve low power consumption.
For example, FIG. 3 illustrates a data pattern having an advantage of low power consumption when charge sharing is used, a composite data pattern, and a data pattern having an advantage of lower power consumption when the charge sharing is not used are respectively applied to first, second and third data ICs TAB1, TAB2 and TAB3. As shown, power consumption of the third data IC TAB3 increases while power consumption of the first data IC TAB1 decreases. When the charge sharing is not uniformly used for the data ICs TAB1, TAB2 and TAB3, power consumption of the third data IC TAB3 decreases while power consumption of the first data IC TAB1 increases.